PHP newbies on the road (4)_PHP tutorial

Getting Started with PHP

4.1 Data Types

PHP supports integers, floating point numbers, strings, arrays and objects. Variable types are usually not determined by the programmer but by the PHP runtime (what a relief!). Of course, if you like, you can also use cast or the function settype() to convert a variable of a certain type into a specified type.

Number

The numerical type can be an integer or a floating point number. You can use the following statements to assign a value to a value:
$a = 1234; # Decimal number
$a = -123; # Negative number
$a = 0123; # Octal number (equal to decimal number 83)
$a = 0x12; # Hexadecimal number (equal to 18 decimal numbers)
$a = 1.234; # Floating point number "double precision number"
$a = 1.2e3; # Double Exponential form of precision number

String

Strings can be defined by fields enclosed in single or double quotes. Note that the difference is that strings enclosed in single quotes are defined literally, while strings enclosed in double quotes can be expanded. Moreover, you can use backslash () in a double-quoted string to add escape sequences and conversion characters to the string. For example:

$first = 'Hello';
$second = "World";
$full1 = "$first $second"; # Generate Hello World
$full2 = ' $first $second';# produces $first $second
$full3="01DC studio,." 2000 copyright." " ;

　Please note the last line, if you need to use double quotes in the string , you can use the backslash character, as shown in this line of statements. The backslash here is used to change the functionality of double quotes.

Characters and numbers can be connected using arithmetic symbols. Characters are converted to numbers using their original position. There are detailed examples in the PHP manual.

Arrays and Hash Tables

Arrays and hash tables are supported in the same way. How you use them depends on how you define them. You can define them using list() or array(), or assign values ​​to arrays directly. The index of the array starts from 0. Although I haven't explained it here, you can easily use multidimensional arrays.

//An array containing two elements
$a[0] = "first";
$a[1] = "second";
$a[] = " third"; // Simple way to add array elements
// Now $a[2] is assigned the value "third"
echo count($a); // Print out 3 because the array has 3 elements Element
// Define an array with a statement and assign value
$myphonebook = array (
"sbabu" => "5348",
"keith" => "4829",
"carole" => "4533"
);
// Oh, forget about the dean, let's add an element
$myphonebook["dean"] = "5397";
// You defined the carale element wrong, let's correct it
$myphonebook["carole"] => "4522"
// Haven't I told you how to use similar support for arrays? Let's take a look at
echo "$myphonebook[0]"; // sbabu
echo "$myphonebook[1]"; // 5348

Some others useful for arrays or hash tables The functions include sort(), next(), prev() and each().

Object

Use the new statement to generate an object:
class foo
{
function do_foo ()
{
echo "Doing foo.";
}
}
$bar = new foo;
$bar->do_foo();

Change variable type

Mentioned in the PHP manual : "PHP does not support (and does not require) defining the variable type directly when declaring the variable; the variable type will be determined based on the situation in which it is used. If you assign the variable var to a string, then it becomes a string. If you assign an integer value to it, it becomes an integer. "

$foo = "0"; // $foo is a string (ASCII 48)
$foo++; / / $foo is the string "1" (ASCII 49)
$foo += 1; // $foo is now an integer (2)
$foo = $foo + 1.3; // $foo is a double Precision number (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is an integer (15)
$foo = 5 + "10 Small Pigs"; // $foo is an integer (15)

If you want to forcefully convert the variable type, you can use the same function settype() as in C language.

4.2 Variables and Constants

You may have noticed that variables are prefixed with a dollar sign ($). All variables are local variables. In order to use external variables in the defined function, use the global statement. And if you want to limit the scope of the variable to the function, use the static statement.
$g_var = 1; // Global scope
function test()
{
global $g_var; // This way global variables can be declared
}

More More advanced is the variable representation of variables. Please refer to the PHP manual. This can sometimes be useful.

PHP has many built-in defined variables. You can also use the define function to define your own constants, such as define("CONSTANT", "value").

4.3 Operators

PHP has the commonly seen operators in C, C++ and Java.The precedence of these operators is also consistent. Assignment also uses "=".

Arithmetic and characters

There is only one operator related to characters:
$a + $b: Add
$a - $b: Subtract
$ a * $b: Multiply
$a / $b: Divide
$a % $b: Modulo (remainder)
$a. $b: String concatenation

logical sum The comparison

logical operators are:
$a || $b: or
$a or $b: or
$a && $b: with
$a and $ b: with
$a xor $b: exclusive or (true when $a or $b is true, false when both are the same)
! $a: non-
comparison operators are:
$a == $b: equal
$a != $b: not equal
$a $a $a > $b : Greater than
$a >= $b : Greater than or equal to
Like C, PHP also has a triple operator (?:). Bit operators also exist in PHP.

Priority

Just like C and Java!

4.4 Control flow structure

　PHP has the same flow control as C. I will briefly introduce it below.

if, else, elseif, if(): endif

if (expression one)
{
. . .
}
elseif (expression 2)
{
. . .
}
else
{
. . .
}
// Or like Python
if (expression 1) :
. . . .
. . .
elseif (Expression 2) :
. . . .
else :
. . . .
endif ;

Loops. while, do..while, for

while (expression)
{
. . .
}
do
{
. . .
}
while (expression);
for (expression one; expression two; expression three)
{
. . .
}
/ / Or like Python
while (expr) :
. . .
endwhile ;

switch

switch is the best for multiple if-elseif-else structures Replacement:
switch ($i)
{
case 0:
print "i equals 0";
case 1:
print "i equals 1";
case 2:
print "i equals 2";
}

break, continue

break breaks the current loop control structure.
continue is used to jump out of the remaining current loop and continue executing the next loop.

require, include

　 Just like #include preprocessing in C. The file you specify in require will replace its location in the main file. When referencing a file conditionally, you can use include(). This allows you to split complex PHP files into multiple files and reference them separately when needed.

4.5 Function

You can define your own function like the following example. The return value of the function can be any data type:
function foo (variable name one, variable name two, . . . , variable name n)
{
echo "Example function.n";
return $retval;
}

All PHP code can appear in function definitions, even definitions of other functions and classes. Functions must be defined before being referenced.

4.6 Classes

Use class models to create classes. You can refer to the detailed explanation of classes in the PHP manual.
class Employee
{
var $empno; // Number of employees
var $empnm; // Employee name

function add_employee($in_num, $in_name)
{
$this->empno = $in_num;
$this->empnm = $in_name;
}

function show()
{
echo "$ this->empno, $this->empnm";
return;
}

function changenm($in_name)
{
$this->empnm = $ in_name;
}
}

$sbabu = new Employee;
$sbabu->add_employee(10,"sbabu");
$sbabu->changenm(" babu");
$sbabu->show();

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